import pyvista as pv
sphere = pv.Sphere()
sphere.point_data['s']=list(range(sphere.n_points))
extracted = sphere.extract_points(
    sphere.points[:, 2] > 0, include_cells=True
)
print(sphere.points[:,2]>0)
# extracted.clear_data()  # clear for plotting
extracted.plot()

ns=self.undeform_mesh.extract_points(item.data()-1,include_cells=False)
pl.add_mesh(self.undeform_mesh,show_edges=True)
pl.add_mesh(ns,style="points",point_size=25,color='b',render_points_as_spheres=True)
